A nonaqueous electrolyte secondary battery (hereinafter, referred to simply as “secondary battery”) is in widespread use as a power supply for mobile devices such as mobile phones, PHSs (Personal Handyphone System), and compact computers because of its high energy density. Further, in recent years, a secondary battery receives attention as a power supply for automobiles such as PHEV (plug-in hybrid electric vehicles), HEV (hybrid electric vehicles) and EV (electric vehicles).
A life required for secondary batteries for mobile devices is about several years; however, a life of 10 years or more, which corresponds to a life of an automobile body is required for an automobile secondary battery. Therefore, a recent demand for an extended life of a secondary battery is high, and an improvement of cycle characteristics of a secondary battery for extending a life has been actively studied.
As a technology for improving the cycle characteristics of a secondary battery, for example, a technology of adding an additive to an electrolyte solution is disclosed in JP-A-2007-188861, JP-A-2008-140683 and JP-A-2014-22335.
Specifically JP-A-2007-188861 discloses that when 4-fluoro-1,3-dioxolan-2-one (FEC) is added to an electrolyte solution, a coating can be formed on a negative electrode, and the diffusion and acceptance of lithium ions in the negative electrode are improved. As a result, precipitation of a lithium metal in the negative electrode is suppressed, and consequently cycle characteristics are improved.
JP-A-2008-140683 and JP-A-2014-22335 disclose that when a coating is formed on a negative electrode by addition of FEC, the decomposition reaction of an electrolyte solution in the negative electrode is inhibited to thereby suppress a reduction in capacity (available capacity). As a result, cycle characteristics are improved.
However, the cycle characteristics of a secondary battery are not always improved only by adding FEC to an electrolyte solution. It has been required to provide a secondary battery having high cycle characteristics more reliably.